Color not coming through glass?
Because I was having the exact same problem, and I mean exact same, I tried lowering my specularity to just .3 and here's the result. While the liquid looks amazing and I think the cup looks ok (too thin now, I'll have to scale the liquid down) there's a large reflection of the plate from the other side. How can I prevent the light reflecting off the plate from also going through the liquid? I would like for light to be diffused inside of the liquid.

I changed the lighting angle and it helped, haha. But there's still an odd reflection.